In the transmission of electrical alternating current through a power line, resistive and reactive losses occur which result in a loss of the amount of power transmitted through the line. These power losses are directly proportional to the resistance or the reactance of the line where the reactance represents the sum of resistance and the difference between the inductive reactance and the capacitive reactance of the system. Because inductive reactance losses are directly proportional to the frequency of the alternating current these losses become more significant in high-frequency electrical transmission systems such as the 400 Hertz ground power systems utilized to provide power to aircraft.
The power loss in moving current through a line caused by resistance becomes dissipated as heat. In a normal alternating current power transmission line, inductive reactance causes the current to lag the voltage in phase. This causes a standing wave to exist on the power line which results in power seemingly lost because the entire current cannot be delivered to the load. Because alternating current power losses are directly proportional to the square of the current, it has been the practice in the past to raise the transmission voltage in order to cause a corresponding reduction in the current flowing in the transmission line for the same power to be delivered to a load. The disadvantage to this solution resides in the fact that it becomes necessary to provide an extra transformer at each load location to reduce the voltage to a value usable by the load.
As mentioned above, inductive reactance power losses occur in an alternating current system because the current tends to lag the voltage in phase which reduces the power ultimately delivered to the load. One approach to compensate for inductive reactance losses in the past has been to introduce capacitive reactance into the line to compensate for inductive reactance losses. Capacitive reactance in a line causes the voltage to lag the current. If capacitors are installed in series with a line such that the amount of capacitive reactance equals the amount of inductive reactance in the line, the line will be considered resonant and will deliver the maximum possible voltage to the load with the system experiencing only resistive losses. However, this system cannot accommodate resistive losses and does not automatically adjust for changes in line load.
It has been found desirable to provide a system which will automatically compensate for power losses resulting in alternating current transmission systems including those resulting from changing line loads which do not require the installation of a transformer at each load to reduce the transmission voltage to an acceptable level and one which will compensate for resistive line losses as well as inductive reactance of a line without regard to line load.